The present invention relates to the field of intraocular lenses (IOLs) and more specifically to a new lens with an improved haptics design for controlled or predictable axial displacement of the optical body in the capsular bag after implantation.
The traditional IOL comprises an optical body and haptics attached to the optical body or the haptics being integrally formed from the same piece of material as the optical body. Polymethylmethacrylate (PMMA) was early found to be an excellent material for such lenses, and especially for the lens body, due to good optical characteristics and good biocompatibility. Considerable efforts have been focused on the haptics design for a number of reasons: the tissue in the eye being rather sensitive to external forces and it is important that the optical axis of the lens body is kept centered in the eye, just to mention a couple of aspects to be considered. This fact is well illustrated by the great number of patents published over the years and which are related to various haptics designs.
In preparation for lens implantation the natural lens is removed from the capsular bag and the bag in most cases is filled with a high viscosity solution, e.g. Healon(copyright) (Pharmacia and Upjohn AB). Then the lens is implanted through an incision, via iris, into the capsular bag and positioned with the haptics contacting the wall of the bag and centering the optical body behind the iris. In order to avoid that the optical body contacts the iris it is common practice that the haptics have a certain forward angulation. e.g. around 5-10 degrees, relative to the optical body. After implantation when the haptics are somewhat compressed in the bag, the lens vaults backwards towards the posterior capsular wall, which in most cases remains after removal of the natural lens. Since the size of the bag differs among the patients requiring a new artificial lens, it is easy to realize that the position of the optical body will differ from one individual to another.
Certain dimensions of the eye, including the position of the capsular bag are measured prior to surgery to give an appropriate basis for a calculation of the dioptre of the IOL to be implanted. If the axial position of the lens body is not completely predictable an error is introduced which is as high as around 0.2 D for each 0.1 mm displacement. Therefore, there is a need for lenses which during implantation are placed in a predicted position and which remain in that position. An improved method for calculation of the correct dioptre is disclosed in pending patent application EP96914495.5. An important parameter is the position of the haptic plane which can be derived from measurements by the ophthalmologist in preparation for surgery, but it is important to consider the effect of the vault resulting from the compression of the haptics. Supporting elements of the implantable lens, i.e. haptics, are well disclosed in the literature for different purposes. For example U.S. Pat. No. 4,778,464 discloses an IOL with supporting elements at a controlled distance form its optic part which together with two rods will interpose the iris. This type of lens is to be fixated by the iris and is of a different type to those disclosed above and which are the subject of the present invention and aimed to be implanted in the capsular bag. Some other IOLs of the iris fixation type are disclosed by the German patent specification DE 2437184 and DE 2538983.
It is a demand for an IOL to be placed in the capsular bag which provides a better optical outcome after cataract surgery irrespectively of the size of the capsular bag or the vitreous pressure which vary considerably between different patients.